Discarding practices and marine mammal by-catch in the Celtic Sea herring fishery

Pelagic fisheries account for 83% of the total number of fish landed into Irish ports, with mackerel Scomber scrombrus, horse-mackerel Trachurus trachurus and herring Clupea harengus constituting 97% of this. Despite the importance of pelagic fish species, there is little published information on discarding practices for most Irish trawl fisheries and no study of marine mammal by-catch. Fisheries scientists accompanied commercial trawlers fishing herring in the Celtic Sea during the 1994/5 season. During the study, 85 days were spent at sea, with 78 tows monitored, amounting to 101h of fishing effort, which was 7% of the total effort in the fishery. Most fishing was carried out in International Council for the Exploration of the Sea (ICES) divisions VIIg01, VIIg02 and VIIa20, and most fish were caught in VIIg01 and VIIa20. The fishery was very selective, with 99.5% of the total weight of the catch being the target species. Mean size (±SE) of herring caught was extremely consistent, ranging from 24.8 ± 2.7cm in October to 26.0 ± 2.0cm in January. Overall, 1270 tonnes of fish were observed being caught, of which 1214 tonnes were landed and 57 tonnes discarded (4.7%). Whiting Merlangius merlangus was the most frequently recorded non-target fish species; mackerel and horse-mackerel were also frequently caught. Four grey seals Halichoerus grypus were caught during the study at a rate of one per 317.5 tonnes of fish or 0.05 seals per tow. This catch rate extrapolates to around 60 seals caught in the fishery, which is not thought to have a significant impact on the Irish seal population.